Two of our botanists recently spent a week collecting ferns on Lord Howe Island. They were adeptly guided by Lord Howe Island museum curator Ian Hutton and joined by Daniel Ohlsen from the Royal Botanic Gardens Victoria. Lord Howe Island is a nature-lovers’ paradise with much of the island protected in reserve and mammal pests recently eradicated. Our fern findings will be detailed in a future blog post but here Lara Shepherd and Leon Perrie discuss the natural history of Lord Howe Island and introduce some of its flowering plants.
Lord Howe Island is a small island (less than 15 km2) located 700 km northeast of Sydney.
The island is an old shield volcano that formed around 7 million years ago but has since eroded to about 1/40th of its original size. Two steep remnant volcanic peaks dominate the skyline in the southern part of the island – Mt Gower (875 m) and Mt Lidgbird (777 m).
Lord Howe Island was one of the last places in the world to be settled by humans. It was first sighted in 1788 by British sailors en route from Sydney to Norfolk Island. The first permanent settlers arrived in 1834 bringing pigs, goats and cats. Mice arrived in 1850 and rats reached the island following a shipwreck in 1918.
These introduced animals wreaked havoc on the island leading to the extinction of at least nine bird species and two plants (it is likely that there were also extinctions of smaller animals, such as invertebrates and lizards).
Inspirational predator control
In 1981, 70% of the island was made a permanent park preserve and a year later the island was made a UNESCO World Heritage site. Feral cats and pigs were eradicated in the 1980s and Aotearoa New Zealand hunters shot all the goats in 1999.
Twenty years later rats and mice became the target of an eradication programme. These initiatives have already had a positive impact – the endemic Lord Howe woodhens (Gallirallus sylvestris), relatives of our weka, were reduced to only 15 birds in 1980, thought to be a result of feral pigs.
Following pig eradication, their numbers slowly increased to around 250 by 2007/2008. However, after the commencement of the rodent eradication, woodhen numbers increased four to five-fold. This suggests that rats were also having a big impact on the woodhens, possibly competing for food.
A recovering biota
It will be interesting to see how the plants and animals recover following the recent rat and mouse eradication, especially the less visible critters such as invertebrates.
Already a cockroach and four snail species, all thought to be extinct on the main island, have been rediscovered. The lack of rodents is also having a positive effect on the native forest with seeds that were previously eaten now germinating in abundance.
Unfortunately, the weeds on the island are likely to also rebound following the rodent eradication. A weed eradication programme has been in place since 2004. It is based on the Aotearoa New Zealand Department of Conservation’s programme for Raoul Island in the Kermadec Islands.
We noticed that the weeds were less dominant on Lord Howe Island than on our recent trip to Norfolk Island, despite the much more challenging terrain for the weeders, as seen in the photos taken by Lara and Leon below.
Unique plants of Lord Howe Island
The plants of Lord Howe Island have affinities to those of Australia, New Caledonia, Aotearoa New Zealand, and Norfolk Island. Despite being a much smaller island than Norfolk Island, Lord Howe Island has many more native vascular plant species (around 240 on Lord Howe Island vs around 180 on Norfolk Island) and more endemic vascular plants (105 on Lord Howe Island vs 46 on Norfolk Island).
This is probably because Lord Howe Island is older, closer to Australia, and has a greater range of habitats. Many of the endemic species occur in the mossy cloud forest on Mts Gower and Lidgbird.
Four genera of plants are endemic to Lord Howe Island (found nowhere else). Three of these genera are palms and contain four species. The most well-known is the kentia palm (Howea forsteriana), which is the most popular cultivated palm in the world. The export of kentia palm seed began around 150 years ago and was once the biggest export from the island.
Pumpkin tree (Negria rhabdothamnoides) is a member of an endemic genus and the only member of its family to form a tree, reaching 8m in height. Interestingly, it is distantly related to African violets and the New Zealand gloxinia/taurepo (Rhabdothamnus solandri).
A puzzling distribution
Despite its name, the Lord Howe wedding lily (Dietes robinsoniana) is a type of iris. Its occurrence on the island has bamboozled botanists – the five other species in the genus only occur in southern Africa. DNA research indicates that it arrived in Lord Howe by long-distance dispersal.
Aotearoa New Zealand relatives
The hotbark tree (Zygogynum howeanum) gained its common name because its bark (and leaves) is hot to chew. It is a distant relative to Aotearoa New Zealand’s horopito (Pseudowintera colorata), which also has a hot peppery taste to the leaves.
There are over 50 species of Coprosma in Aotearoa New Zealand, making it the centre of diversity for the genus. Lord Howe has six species, including stinkwood (Coprosma putida), whose leaves and fruit smell terrible, and Coprosma huttoniana, named for Ian Hutton, our guide on the island.
The mountain daisy (Olearia ballii) is endemic to Lord Howe Island, where it is common on the higher mountains. It is a relative of New Zealand’s tree daisies.
Lord Howe has 12 orchid species. Some species, like the onion orchid, are shared with Aotearoa New Zealand or Australia. The drooping cane orchid (Dendrobium moorei) is endemic to Lord Howe and has large flowers compared with its Aotearoa New Zealand relative winika (Dendrobium cunninghamii). It only grows on the mountains above 400m elevation.
Lord Howe Island has two endemic species of mountain rose, which are in same genus as our rātā and pohutukawa (Metrosideros). They are both potentially at threat from myrtle rust which has been detected twice on the island but eradicated both times.
Lignum vitae (Sophora howinsula) is closely related to and looks very similar to Aotearoa New Zealand’s large-leaved kōwhai (Sophora tetraptera). Seeds of the ancestor of lignum vitae likely floated to Lord Howe Island in the last few million years.
Ian Hutton for guiding us and sharing his wealth of knowledge about Lord Howe ferns (and other plants, birds, fish as well as the history of the island).
Jenny and Brian Solomon for gifting us the guidebook on Lord Howe ferns, which was written by Ian, and inspired us to research these fascinating plants.
Lord Howe Island resident Tim Solomon kindly organised a source of newspaper (it is a scarce commodity on the island), enabling us to press our fern specimens.
The Lord Howe Island Board allowed us to stay at the Research Facility and approved our fern research.